The present invention relates to an optical head for recording or reproducing information onto/from an optical information recording medium.
In the following Patent Documents 1, 2 and 3 is described an optical head.
In the Patent Document 1 is made the following description: an object is “to provide an optical pickup enabling to deal with plural numbers of recording media, each having a different recording density, such as, CD, DVD and a next generation DVD, by means of plural numbers of objective lenses and a light source of plural numbers of wavelengths”, and “Tilt of the objective lens, generating when manufacturing the optical pickup, is compensated with driving of an object lens actuator. This actuator can be made lightweight than the conventional operation portion having plural numbers of objective lenses, by dividing magnetic circuits provided in the operation portion into, i.e., a focusing direction and a tracking direction. Also, disposing the plural numbers of objective lenses by taking the difference of operating distances into the consideration thereof, it is possible to prevent the objective lens having a short operating distance from touching on the recording medium.”
Also, in the Patent Document 2 is made the following description: “With using a tracking error signal producing means for producing a tracking error signal, i.e., a signal to be used for control of irradiating a beam on a desired track, wherein said light detecting means has plural numbers of light receiver portions, said plural numbers of beams irradiate different positions in the direction perpendicular to the track, and said tracking error signal producing means produces a push-pull signal by conducting differential operation on the signals outputted from said light receiver portions; thereby controlling the signal obtained from said plural numbers of beams.”, and “With such the structure as was mentioned above, it is possible to obtain a preferable TE signal, which is less influenced by a stray light upon reflection from a protection layer of the information recording medium, and thereby providing an optical head device for enabling to recording/reproducing of information with a high reliability.”, and “Also, the reflection surface generating the stray light should not be restricted to the surface of a transparent substrate, but in case where the optical recording medium has plural numbers of recording surfaces thereon, the stray light is generated from other than the recording surface recording or reproducing the information thereon/from. In such case, the present invention is also effective.”